#include <fstream.h>

   int N, cnt;
   char prim[2000005];

   int main()
   {
       int i, j;

       ifstream f("ciur.in");
       ofstream g("ciur.out");
       f>>N;
      for (i = 2; i <= N; ++i)
	   prim[i] = 1;
      for (i = 2; i <= N; ++i)
	   if (prim[i])
	   {
	       ++cnt;
	       for (j = i+i; j <= N; j += i)
		   prim[j] = 0;
	   }

	g<<cnt;

       return 0;
   }